1. Technical Field
The present invention relates to pipelines, which are laid onto the seabed, and more precisely a method for laying a pipeline onto a seabed from a lay barge, the pipeline having an inner corrosion proof metallic cladding that is closely fitted with metallic contact to an outer pipe material that is less corrosion proof. With the method according to the invention, a pipeline of the type mentioned can be arranged onto and laid into place from a laying drum on the lay barge.
2. Description of the Related Art
With an increasing need for transporting unprocessed well streams from underwater facilities, and more frequent occurrence of aggressive fluids with need to be transported, there is an increased demand for corrosion proof pipelines. However, the cost for pipelines of corrosion proof material has dramatically increased, and less expensive alternatives are therefore being sought after.
One such less expensive alternative is a pipeline of carbon steel with an inner more corrosion proof cladding. The strength of the carbon steel is thereby combined with the corrosion resistance of the cladding. The cladding is typically produced from a corrosion proof steel, a so-called stainless steel, and the cladding typically has a thickness from 1 to 7 mm, most typically about 3 mm. The cladding is fitted to the carbon steel pipeline's interior surface, either with mechanical contact or with metallurgical bonding by means of hot rolling (roll welding), welding, brazing or clad welding. The obviously least expensive alternative is that the inner cladding is fitted mechanically tightly against the carbon steel pipeline with metallic contact without any room in between. However, this embodiment has proven to be inadequate with respect to laying by reeling out from a pipe laying drum onboard a lay barge because the inner cladding becomes deformed by so-called “buckling/wrinkling”, such as bulging, buckling, and subsequent possible fracturing. Such deformation will result in that the inner cladding will loosen from the carbon steel pipeline's interior surface, causing it to lose its ability to resist the impact during operation of the pipeline. This represents a problem, which needs to be solved.
No prior art is known that can solve the above-mentioned problem, which previously appears not to be particularly focused upon. Background art is represented by the patent publications US 2003/0056954 A1, which relates to a method for maintaining a pipeline in operation; U.S. Pat. No. 6,142,707, which relates to direct electrical heating of a pipeline; and EP 1233143 A1, which relates to coiled tubing operations inside wells. The patent publications describe an inner pipe installed within an outer pipe, but with spacing between the pipes and for most embodiments the inner pipe is a composite coiled tubing. The prior art referred to above relates to problems other than the problem underlying the present invention.